Distance-measuring devices of the above-mentioned type serve to measure distance employing optical means. Distance-measuring methods are generally known which, for example, make use of the runtime of a light-modulation signal that is configured, for instance, as a light pulse, a sinusoidal wave or a pseudo noise, and/or the phasing of a coherent optical beam of the type generated, for instance, by a laser. Likewise known is the familiar method of laser triangulation. These methods can be employed for distance measurement on an as-needed basis. For this purpose, the distance-measuring device provides for an appropriately configured measuring apparatus that is arranged in the housing and that makes use of an optical measuring beam by means of which the distance to the target point can be measured contactlessly. Thus, for instance, German revised patent DE 100 51 302 CS or German patent specification DE 101 12 833 C1 disclose the configuration of a suitable measuring apparatus.
A distance-measuring device of the above-mentioned type can be especially advantageously provided in the form of a handheld device in which the housing is configured for handheld use, especially in terms of its shaping, dimensions and the like. Fundamentally speaking, the distance measured to a target is determined with reference to a housing-internal reference zero point. The distance-measuring device, however, is handled in such a way that the user places the housing or an extension thereof against an object, for example, against a wall or on the ground, whose distance to the target is to be measured. For this purpose, the housing has at least one reference stop that can be selected by the user in order to carry out the measurement. Such a reference stop can be an integral part of the housing, or else it is connected to the housing as a housing extension, or it can be connected to the housing for example, as a tripod. The reference stop can be selected by the user by activating, pulling out or attaching the housing extension on the housing. If applicable, a reference stop can also be operated by means of an operating and input array arranged on the housing. An operating and input array can be configured, for example, in the form of a keypad or the like. Through such a selection by the user, a fixed addition constant that is decisive for the reference stop is added to the distance between the reference zero point and the target so that the correct distance between the object and the target can be displayed to the user once the distance has been measured. The measured distance is normally shown on a visual display. The visual display is usually also coupled to the operating and input array in order to indicate an operating state of the distance-measuring device or the like on the visual display.
In the state of the art, there are various approaches aimed at increasing the basic measuring accuracy of such distance-measuring devices of the above-mentioned type. For instance, German patent application DE 101 57 378 A1 discloses a distance-measuring device in which a temperature-related curvature of the housing is compensated for by deflecting the transmitting and receiving path of the distance-measuring device. German patent application DE 102 32 878 A1 shows a distance-measuring device in which distances with predefinable measuring uncertainties can be measured in that a distance-dependent measuring uncertainty is stored as data in a storage medium, for example, in the form of a characteristic.
Aside from such device-related measuring uncertainties, however, the greatest risk of errors arises when a distance-measuring device is inadvertently handled incorrectly. For instance, German patent DE 102 39 435 B4 discloses a distance-measuring device in which an operating unit that serves for emitting an optical signal allows the light source of the measuring device to be switched on and off.